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All those chemical elements that belong to the group I of the periodic table are known as alkali metals. As alkali metals are highly reactive elements, they are mostly found in the form of compounds and not in an elemental form. The chemical elements which are categorized into alkali metal group are arranged in increasing order of atomic number as: Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Caesium (Cs) and Francium (Fr). Hydrogen is placed at the top of the alkali metals group but most of its properties are very different from those of alkali metals. Only under extremely high pressure, hydrogen shares some properties with alkali metals. To know more read on:

• Interesting Facts about Sodium
• Interesting Facts on Potassium

Physical Properties of Alkali Metals

The physical properties of alkali metals are very similar with other metallic elements. However, some of the alkali metal properties are very different. Like, the densities of alkali metals are much lower when compared to other metals. Unlike other metals, all the elements of alkali metal group are soft substances and can be cut with the help of a knife. In any given period of the periodic table, the atomic radii of the alkali metals is largest. Alkali metals are good conductors of heat and electricity. Both the boiling point as well as the melting points of alkali metals are very low. Except for caesium, which has a light golden color, alkali metals are silvery white in color. Other typical alkali metal properties are that they are lustrous and have ductile and malleable properties. Actually, alkali metals have a shiny surface but they get tarnished very easily, as a result of oxidation with the atmospheric oxygen and their appearance becomes dull. On burning, alkali metals give out colored flames. Two of the alkali metals, potassium and rubidium exhibit weak radioactive properties. To get some more information on the properties of alkali metal sodium read on sodium properties - chemical and physical properties of sodium.

Chemical Properties of Alkali Metals

The atom of any given alkali metal has only one electron in its outermost orbit. Each of the alkali metals are ready to lose this lone pair of electron to form a univalent cation. The chemical reactivity of alkali metals increase as we move from the top to the bottom of the group. Like any other metals, ionization potential of the alkali metals is very low. In fact, alkali metals have the lowest ionization potential among the elements of any given period of the periodic table. Electronegativity of alkali metals is also of a very low range. When alkali metals react with non metals, they form ionic salts. Following are some of the important reactions of alkali metals:

Reaction with Oxygen
Any alkali metal when comes in contact with air or oxygen, starts burning and oxides are formed in the process. At the end of the chemical reaction, lithium gives lithium monoxide(LiO), sodium gives sodium peroxide (Na₂O₂) and other alkali metals give superoxides (that is, each alkali metal atom forms bonds with two oxygen atoms). Oxides of alkali metals are basic in nature and are soluble in water and form alkali metal hydroxides.

Reaction with Hydrogen
When alkali metals react with hydrogen, then ionic hydrides are formed. The ionic nature of the hydrides increase as we move down from lithium to caesium. The stability of the hydrides thus formed, reduces with the increase in the atomic numbers of alkali metals. These hydrides have strong reducing properties.

Reaction with Halogens
Alkali metals react with elements of halogen group of the periodic table to form halides. Except lithium iodide all other halides are ionic in nature. To some extent, lithium iodide is covalent in nature as the bonding occurs between the smallest cation and the largest anion. As a result, the large iodide anion gets polarized. All the halides of alkali metals readily dissolve in water except lithium fluoride (LiF).

Reaction with Water
Alkali metals react with water to form hydroxides and hydrogen gas is released in the process. The reaction is so vigorous in nature that the hydrogen gas produced during the reaction catches fire. Lithium is the only alkali metal that reacts slowly with water. The hydroxides of alkali metals possess strong basic properties. The strength of the basic properties of alkali metal hydroxides increase with rise in atomic number of the alkali metals.

Knowledge of all these distinctive alkali metal properties helps us to prepare a large variety of essential alkali metal compounds. Sodium hydroxides, sodium chloride and sodium carbonate are some of the most useful compounds of alkali metals that are used in various industries.